High aperture four component objective of the gauss type



SEARCH ROOM July 21, 1953 HIROSHI ITO HIGH APERTURE FOUR COMPONENT OBJECTIVE OF THE GAUSS TYPE Filed June 29. 1951 JNVENTOR HIROSHI ITO ms AT TORNE I Patented July 21, 1953 HIGH APERTURE FOUR COMPONENT OBJECTIVE OF THE GAUSS TYPE Hiroshi Ito, Setagaya-kn, Tokyo, Japan, assignor to Canon Camera Company, Ltd., Chuouku, Tokyo, Japan, a corporation of Japan Application June 29, 1951, Serial No. 234,354 In Japan January 31, 1951 7 Claims.

The present invention relates to an improved high aperture objective of Gauss type for use in a camera.

The object of the present invention is to provide such a camera lens with highest resolving power and aperture and free of oblique spherical aberration (i. e., coma) throughout the image plane with an including field of some 30 degrees.

The means to remove the spherical aberration from an objective of Gauss type and increase its aperture is so simple that there are already in existence several such objectives whose aperture is above F:l.5. However, a common defect in these lenses is that it is next to impossible to remove the oblique spherical aberration throughout the picture area with the result that when any such lens system used in a state of open stop, the picture is subject to considerable unpleasant shading-off. This remarkably lowers its resolving power when a photograph is taken of an object with low contrast. In the present invention, there is applied to the lens system of some 30 including field, a principle similar to that disclosed in my copending U. S. application 234,353, filed June 29, 1951, whereby the above-mentioned common defect of prior known photographic objectives of the Gauss type is removed, to produce the objective of the instant invention having both a high aperture and a very high resolving power.

In accordance with the instant invention, of two cemented lenses of meniscus shape situated opposite to each other'across the stop, the one on the object-side shall act in concave manner to correct spherical aberration on the axis, while the meniscus lens on the picture-side shall act in convex manner, as is the case in the objective disclosed in the above-mentioned copending application. In the present invention, the refractive power I a minimum, and for that purpose, studies have clarified that it is most advantageous for the cemented object-side compound meniscus lens to be composed of preferably three single lenses. Further the inventor has confirmed that for the purpose of removing oblique spherical aberration, the radius of curvature of the first face of the cemented image-side compound meniscus lens, that is the concave face facing to the stop, should be, in its absolute value, from 0.25 to 0.45 fold of the focal length, and that the axial thickness of the cemented object-side compound meniscus lens should be larger than 0.25 fold of the focal length. r

The foregoing and other objects and features of the invention will be understood more fully and clearly from the following detailed description of two illustrative embodiments thereof taken in connection with the appended drawing in which:.

Figure 1 is an axial section throughthe lenses of the first illustrative embodiment of the objective of the invention in which the front meniscus compound lens consists of three cemented lenses; and

Figure 2 is an axial section through the lenses of the second illustrative embodiment of the objective of the invention in which both the front and rear meniscus compound lenses each consist of three cemented lenses.

The objective of Figure 1 consists of four lens units, I, II, III and IV, axially aligned and separated from each other by air spaces d2, dB and d9 respectively. The front lens unit I is a single positive lens L1 of axial thickness di and of a front radius n and a rear radius T2. The second lens unit II is a compound lens having two positive lenses L2 and L3, of axial thickness d3, front radius 13 and rear radius r4, respectively, (14, T4 and r5, cemented to, each other on n, and dispersive lens L4 of axial thickness (is and a front radius 1'5 and a rear radius of T6 cemented to lens L3 along the surfaces of radius n. The third lens 'unit 111 consists of a dispersive lens L5 having an axial thickness d7, a front surface of curvature n, the latter surface being axially spaced at do from the rear surface of unit II, and a rear radius T8, to which rear surface-of lens L5 is cemented the collective lens Ls having a front surface of radius 1's, a rear surface of radius re and an axial thickness of da. Axially spaced the distance do from the rear surface of lens La is the positive lens L7 of axial thickness die and of a front radius no and a rear radius r11.

The constructional data of the coma corrected objective of this invention of my first illustrative embodiment, for a focal length of 1.00, an including field of 30 degrees and aperture of F/1.5, including the refractive indices 12,, of the individual lenses and the Abb numbers V thereof, is as follows, where the plus sign before a radius indicates the radius has a curvature convex toward the front, that is object side, of the objective and the minus sign indicates curvature concave the front:

7 d L 1 V 7 0. 822 I d1 =0.105 L1 1.6228 56.9

d: =0. 002 rs 0.440

(is =0.085 L: 1.6385 55.5 n 0.805 II d4 =0.190 L3 1.5163 64.0

d =0.020 L4 1. 6880 31. 1 rs 0. 252

11 0.190 77 -0. 310 d7 =0. 015 L5 1. 5317 48. 9 III Ta 0. 572

d! =0.103 Ls 1.6584 50.8 To -0. 440

I1 =0.002 r1o= 1. 500 IV d1o=0. 060 L1 1.6385 55.5

The objective of Figure 2 similarly comprises four lens units I, II, III and IV similarly air spaced and aligned axially, with the difference that unit III of this embodiment here consists of three lenses cemented to each other. The constructional data for an illustrative embodiment of a focal length of 1.00, an including field of 25 degrees, and an aperture of F:l.4, is as follows:

1' d L m V n 0.855 I v d; =0.105 L1 1.6204 60.3

d; =0.085 L: 1.6386 55.5 n 0. 900 II d4 =0.178 La 1.5163 64.0

(is =0. 020 L4 1. 6727 32. 2 To 0. 247

do =0.l90 r7 0. 304

I11 =0.069 Ls 1.5891 61.2 Ta =0-227 III do =0.039 Lu 1.5263 51.0

do 0-058 L1 1.6385 55.5 no 0. 539

d=0. 003 f1 1.300 IV dn=0. 065 L 1. 6385 55. 5

What I claim is:

1. A coma corrected high aperture objective of maximum resolving power comprising a pair of collective lenses enclosing an object-side meniscus compound lens and an image-side meniscus compound lens, the four lenses being axially aligned and air separated, in which the object-side compound lens consists of three individual lenses having respective adjacent faces of the same curvature cemented to each other, the cemented surface thereof nearest the image side of the objective having a curvature concave to the object side of the objective, and the image-side meniscus lens consists of at least two individual lenses having respective adjacent faces of the same curvature and cemented to each other, the object side concave surface of the image-side meniscus compound lens has a radius of from 0.25 to 0.45 times in its absolute value the focal length of the objective, and the axial thickness of the objectside meniscus compound lens is between 0.25 and 0.295 times the total focal length of the objective.

2. An objective according to claim 1 in which for a refractive power of unity of the objective, the refractive power of the cemented surface nearest the image side of the objective of the object-side meniscus compound lens lies between I substantially 0.08'7 and 0.094 in its absolute magnitude, and the refractive power of the cemented surface nearest the object side of the objective of the image-side meniscus compound lens lies between substantially 0.22 and 0.28 in its absolute magnitude.

3. An objective according to claim 1 in which the axial thickness of the object-side compound meniscus lens is between 0.25 and 0.295 times the focal length of the objective and in which, for a refractive power of unity of the objective, the refractive power of the cemented surface nearest the image side of the objective of the objectside meniscus compound lens is from -0.087 to 0.094 in its absolute magnitude while the refractive power of the cemented surface nearest the object side of the objective of the image-side meniscus compound lens is from 0.22 to 0.28 in its absolute magnitude.

4. A coma corrected objective over an including field of 30 degrees comprising two compound meniscus lenses with their concave exterior surfaces toward each other, two collective lenses [Focal length 1.00 F:l.5 Including field 30] r 11 no V (is =0. 020 1. 6889 31. 1 r 0. 252

(is =0. 103 1. 6584 .50. 8 n 0. 440

lil0=0. 000 1. 6385 55. 5 T 0. 846

follows, where r is the radius of the lens surface.

d the axial distance between successive lens surfaces, 11 the indices of refraction and V the Abb numbers of the lens glasses:

[Focal length 1.00 F:1.4 Including field 25] r d 1m V d1 =0.069 1.5891 61.2 rs 0. 227

da =0.039 1.5263 51.0 n =5. 710

do =0.058 1.6385 65.5 m=0. 539

dn=0.065 1.6385 55.5 m= 0. 689

6. An objective according to claim 1 in which the axial thickness of the object-side meniscus lens is substantially 0.295 times the total focal length of the objective, the refractive power at the cemented surface nearest the image side of the objective of the obj ect-side meniscus lens is subthe refractive power of the cemented surface near-- est the object side of the objective of the image side meniscus lens is substantially 0.221 in its absolute magnitude.

7. An objective according to claim 1 in which the axial thickness of the object-side meniscus lens is substantially 0.283 times the total focal length of the objective, the refractive power at the cemented surface nearest the image side of the objective on the object-side meniscus lens is substantially 0.0874 in its absolute ma nitude, and the refractive power at the cemented surface nearest the object side of the objective of the image-side meniscus lens is substantially 0.277 in its absolute magnitude.

HIROSHI ITO.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,708,863 Bertele Apr. 9, 1929 1,779,257 Lee Oct. 21, 1930 2,186,621 Bertele Jan. 9, 1940 FOREIGN PATENTS Number Country I Date 786,127 France June 3, 1935 470,522 Great Britain Aug. 17, 1937 553,844 Great Britain June 8, 1943 

